High frequency filter, combiner and like arrangements



B. M. SOSIN Jan. 22, 1957 HIGH FREQUENCY FILTER, COMBINER AND LIKE ARRANGEMENTS 2 Sheets-Sheet 1 Filed Jan. 24, 1952 Jan. 22, 1957 B. M. sosm 2,779,000

HIGH FREQUENCY FILTER, COMBINER AND LIKE ARRANGEMENTS Filed Jan. 24, 1952 2 Sheets-Sheet 2 amil m1 HIGH FREQUENCY FILTER, COIVIBINER AND LIKE ARRANGEMENTS Boleslaw Marian Sosin, Great Baddow, Chelmsford, England, assignor to Marconis Wireless Telegraph Company Limited, London, England, a company of Great Britain Application January 24, 1952, Serial No. 267,961

Claims priority, application Great Britain February 2, 1951 4 Claims. (Cl. 333-6) According to this invention a filter, combiner or like circuit arrangement for use on high frequencies comprises a four arm bridge circuit with a T-connected'stub in each of two opposite arms, one pair of external connection points in one of the remaining arms, connection points for the connection of a balancing impedance in the other remaining arm and another pair of external connection points in one diagonal, the connections of the bridge and the impedances of the stubs being constituted by distributed reactances and resistance presented by a concentric tubular conductor structure.

In embodiments with three pairs of external connection points the third pair, together with an associated isolating stub, is provided in the second diagonal of the bridge.

An important, though by no means the only application of the invention is to short wave video and sound modulated signal systems.

The invention is illustrated in the accompanying drawings in which Fig. l is a circuit representation of one embodiment and Fig. 2 a schematic representation showing the circuit of Fig. 1 actually embodied in a tubular conductor structure. In order adequately to co-relate these two figures corresponding reference numerals are applied to corresponding parts of the conductor representations and corresponding reference letters indicate the various impedances.

Referring to Fig. 1 the bridge circuit therein shown comprises four arms of which the opposite arms containing the conductor lengths 3, ,5 and 1, 7 respectively include T connected stubs. One of these stubs consists of an impedance Z3 and the impedances Z1, Z2 (in the cross bar of the T) these impedances being of electrical lengths 0 and 0 respectively. In the figure Z1 is shown open circuited at its far end and Z2 short circuited at its far end. Z1 may however be short circuit ended. In the former case (Z1 open) 0 is made slightly less than a quarter of a wave length long at the operating frequency or slightly less than an odd multiple thereof: in the latter case 0 is made slightly less than a half wave length long at the operating frequency or slightly less than an integral multiple thereof. In either case 0 is made short and 0 may be any length.

The T connected stub in the opposite arm arranged to have an input impedance whichis the reciprocal of that of the above described T connected stub and consists of impedances ZsR, ZIR, and Zzn of lengths 0 0 and 0 respectively. The term reciprocal is used herein nited States Patent'O ice in its mathematical sense as explained for example in the text by Guillemin on The Mathematics of Circuit Analysis (Massachusetts Institute of Technology, John Wiley & Son, Inc, New York). Corresponding to Z2 being short circuit ended, Zzn is open circuit ended. Z112 may be short circuit ended in which case 0 is made slightly less than a quarter of a wave length at the operating frequency, or slightly less than an odd multiple of a quarter wave length long. Zm may however be open circuit ended in which case 6 is made slightly less than a half wave length long or slightlyless than an integral multiple of a half wave length long. In either case 0 is made short and 0 may be any length.

The 'third arm of the bridge, containing conductor lengths 1 and 5 contains the output connection terminals 0, the output circuit being represented (in Fig. 1 but not in Fig. 2) as an output tubular line OT leading, for example to a transmitting aerial (not shown). The corner of the bridge between this arm and the arm containing the stub Z3, Z1, Z2 is earthed.

The fourth arm of the bridge contains connection points XX between which a balancing resistance R may be connected through a matched cable K. The cable and resistance are represented in Fig. 1 but not in Fig. 2 where only the points XX are indicated. The cable may, however, be accommodated between the tubes 3 and 4 in Fig. 2 or on the outside of the tube 7.

One pair of input connection points is constituted by the ends of one diagonal of the bridge and in Fig. 1 an input line L1 which may carry, for example a video modulated high frequency wave or other wide. band input, is indicated. A second pair of input connection points is constituted by the ends 12 of the other diagonal and again in Fig. 1 an input line L2, which may carry, for example, a sound modulated or other narrow band input adjacent the wide band input in frequency, is indicated. Across these terminals 1 is connected an isolating stub (marked Zrsor.) short circuited at its far end by a connection 11 and which should be a quarter of a wave length at the operating frequency or an odd multiple thereof, long.

By suitable choice of the lengths 6s and 03a the narrow band frequency can be either below or above the wide band frequency. Also, in some cases the narrow and wide band inputs may be interchanged.

Fig. 2, which will be found largely self-explanatory from the correspondence of numeral and letter references with those of Fig. 1 shows the way in which the circuit of Fig. 1 is embodied in a structure composed entirely of concentric tubes and supporting and spacing insulators INS. All the parts of Figs. 1 and 2 are identified by similar references and the impedances Z1, Z2, etc. are marked in Fig. 2 as well as in Fig. 1. There are two T connected stubs electrically in Fig. 2, one is the stub consisting of the impedances Z1, Z2 and Z3 and the other is the stub consisting of the reciprocal impedances ZIR, Zzn and Z312. All these impedance references will be found in the appropriate places in Fig. 2. While the T con nected stubs do not have the appearance of the T connected stubs from the mechanical point of view in Fig. 2, they are there, nevertheless, as electrical stubs and, indeed, much of the ingenuity and value of this invention are to be found in the way in which the complex circuit of Fig. 1 has been mechanically embodied in the convenient structure of Fig. 2. As will be seen the terminals 12 are concentric as are the terminals 11 and 0, the outer terminals of 12 and 0 being constituted in each case by the periphery of a hole in the appropriate tube. The parts 9, 10 and 11 (Fig. 2) are short circuiting rings provided for adjustment purposes and are slidable as to position, the construction at 10 allowing the tube 7 to'be slide endwise to adjust the value of Zm while a sliding joint at 12 and a push rod 13 enable adjustment of the length of Zn;

to be effected. A sliding joint at 14 and a push rod provide for adjustment of the length of Z1 for operation on any working frequency. The lengths in question are not particularly critical, the important thing, being that they must not be quarter Wave lengths or half. Wave lengths (as the case may be) at any working frequency applied thereto. It will be noted that in cases where there is more than one frequency the said frequencies are closely adjacent. The structure is split, i. e. mechanically diyidable along the line YY (Where face flanges are indicated) so that the parts to the left of the chain line can be. removed to allow those to the right of it tov be adjusted.

Where two inputs are not required,,i. e. in: the case: of a filter, the input terminals 12- may be dispensed with, in which case, if the outermost tube 6 is omitted and the tubes 5 and 7 connected together, the arrangement be comes a switching type filter of narrow pass band or narrow stop band characteristics (depending upon the length chosen for 03 and 63a) i. e.. afilter which switches from output to balancingresistance and thus appears always matched at the input. Alternatively, the same re.- sults can be achieved by dispensing with terminals 11 and connecting the tubes 1 and 3.

Again by dispensing with terminals 1.2 and connecting tubes. 5 and 7 as before, but using the terminals 0. as input terminals. and the terminals 11 as, output terminals the filter may be used asa stop or. trap filter eliminating a desired wide or narrow signal band-e. g. videoor sound signals from a partially mixed outputin dependence upon the lengths chosen. for 0a and 03R- Such an arrangement may be made of quite small, dimensions. Similar results can be achieved. by dispensing with terminals 11, connecting the tubes 1 and 3 and using; 12 as outputterminals and 0 asv input terminals.

The invention provides important practical advantages which are. extremely difiicult if not impossible to achieve with known arrangements. There are no condensers or other lumped. impedances to produce, large voltage differences. and insulation. difliculties; adjustment is easily effected, mostly from outside the structure thus. allowing final and accurate trimming to be eifected while ameasuring signal, or actual useful power is present; the corners of. the bridge are brought virtually to the same point physica1ly-this fact. enables. an actual. embodiment to accord closely with theoretical design data; the balancing resistance is connected by a matched transmission line (the cable). and is thus effectively at the central junction, so that. the actual resistance can be outside. the. structure; the. T-connectedv stubs. give high efficiency and low losses without having. to be physically large; the; IEClPIOCflls arms of the bridge can be. made reciprocal to ahigh degree of accuracy because the lower ends of the stems? of the Ts are brought to. the centralv junction and adjustment to virtually exact. reciprocal values is comparatively easy; in the case of a combiner for wide and narrow band inputs either can be of the higher frequency, as may be desired; the parts of the stubs where losses occur are constituted by identical tubes so that the stub impedances remain closely reciprocal even at resonance, where, resistance isv the governing factor; and the construction ale lows of forced coolinge. g. forced air or water cooling if required.

I claim:

1. A high frequency filter, combiner or like circuit arrangement comprising a four arm bridge circuit in.- cluding concentric tubular conductor structures with a T-conne,cted stub in each of two opposite arms, one pair of external connection points in one of the. remaining arms, connection points for the connection of a balancing impedance in. the other remaining arm and. asecond pair of external connection points in one diagonal, the arms of the, bridge circuit being constituted by the impedance of the. stubs and resistance presented bythe concentric. tubular conductor structures in which one off the T- 4: connected stubs has an input impedance which is the reciprocal of that of the other, said other stub comprising three impedances (Z1, Z2, and Z3) of which Z1 and Z2 are in the cross bar of the T, the concentric tubular conductor structure constituting impedance Z1 being open circuited at its far end and the concentric tubular conductor structure constituting impedance Z2 being short circuited at its far end, Z1 constituting an impedance equivalent to a circuit having an electrical length slightly less than an odd number, including one, of quarter Wave lengths long at the operatingfrequency and Z2 constituting an impedance equivalent to a circuit having an electrical length which is short in relation to the wave length of the operating frequency.

2. A high frequency filter, combiner or like circuit arrangement comprising a four armbridge circuit including concentric tubular conductor structures with a T-connected stub in each of two opposite arms, one pair of external connection. points in one of the remaining arms, connection points for the connection of a balancing impedance in the other remaining arm and a second pair of external connection points in one diagonal, the arms of the: bridge circuit being constituted by the impedances of the stubs and resistance presented by the concentric tubular conductor structures in which one of the T-connected stubs has an input impedance which is the reciprocal of that. of the other, said other stub comprising three impedances (Z1, Z2, and Z3?) of which Z1 and Z2 are in the cross bar of the T, the concentric tubular conductor structure constituting impedance Z1 being short circuited at its far end and the concentric tubular conductor structure constituting impedance Z2 being short circuited at its far end, Z1- constituting: an impedance equivalent to a circuit having an. electrical length slightly less than a whole: number, includingone, of half wave lengths long at. the. operating: frequency and Z2 constituting an impedance equivalent to a circuit having an. electrical length which is short in relation to the Wave length.

3; A. high frequency filter, combiner or like circuit structure composed entirely of concentric tubes and supporting and spacing: insulators, said. structure embodying a four arm bridge circuit including concentric tubular conductor structures with a T-connected stub in: each of twoopposite arms, one pair ofexternalconnection points in one of the remaining arms, connection points for the connection of. at balancing: impedance in: the other remaining arm andLa second pairof external connectionpoints in one diagonal; the: arms. of 'thebridge circuit being constituted by the impedancesv of. the stubs and resistance presented by the. concentric tubular conductor structures, in which one of the T-connect-ed stubs has an input impedancewhiclris the reciprocal of that of the other, said other: stub comprising three; impedances (Z1, Z2, and Z3) of which Z1 and Z2 are in the cross bar of the T, the concentric tubular conductor structure constituting impedance Z1 being open circuited at its far end and the concentric tubular. conductor structure constituting impedance Z2 being short circuited' at its far end, Z1 constituting an impedance equivalent to a circuit having an electrical length slightly less than an odd number, ineluding one, of quarter wavelengths long at the operating frequency and-Z2 constituting an impedance equivalent to a circuit having an electrical length which is short in relation to the wave length of the operating frequency 4; A high frequency filter; combiner or like circuit structure composed entirely of'concent'ric tubesand supporting and spacing insulators,- said" structure embodying a four armbridge circuit including concentric tubular conductor structures with a T-connected stub in each of two opposite arms, one'pair of external connection points in one of the remaining arms, connection points for the connection of a balancing impedance in the other remaining arm and a second pair of external connection points inone diagonal, the arms of the bridge circuit being constituted by the impedances of the stubs and resistance presented by the concentric tubular conductor structures, in which one of the T-connccted stubs has an input impedance which is the reciprocal of that of the other, said other stub comprising three impedances (Z1, Z2, and Z3) of which Z1 and Z: are in the cross bar of the T, the concentric tubular conductor structure constituting impedance Z1 being short circuited at its far end and the concentric tubular conductor structure constituting impedance Z2 being short circuited at its far end, Z1 constituting an impedance equivalent to a circuit having an electrical length slightly less than a whole number, including one, of half wave lengths long at the operating frequency and Z2 constituting an impedance equivalent to a circuit having an electrical length which is short in relation to the wave length of the operating frequency.

Masters Jan. 24, 1950 Herold Apr. 22, 1952 

